1. Field of the Invention
The present invention relates to an information distribution system for distributing information over a radio transmission channel, and to related technology thereof.
2. Description of the Related Art
As a system for distributing information to a mobile object such as a vehicle, via a radio transmission channel, VICS (Vehicle Information and Communication System), which distributes road information to the vehicle of a user using a radio beacon, a light beacon or an FM multiple broadcast is known. Also along with the spread of cellular phones, the Internet and wireless LAN (Local Area Network), systems for distributing information to many unspecified movable bodies in a relatively narrow communication area using a wireless LAN conforming to IEEE 802.11 (Institute of Electrical and Electronics Engineers Standard 802.11) have been proposed. This type of system is disclosed in Japanese Patent Kokai No. 2003-317187 and Japanese Patent Kokai No. 2001-184595.
Compared with an unmoving receiving terminal, the quality of distribution information received by a moving receiving terminal generally tends to deteriorate more easily. Therefore if a transmission terminal broadcasts distribution information to many unspecified receiving terminals and the receiving terminals do not reply with the ACK (Acknowledgment) of the data to the transmission terminal, then highly reliable information distribution is difficult since the transmission terminal does not retransmit the data even if a data receive error occurs to the moving receiving terminal. Also when the transmission terminal broadcasts the distribution information, the receiving terminal cannot always receive the distribution information from the beginning of the data, but may receive it from the middle of the distribution information, which diminishes the advertisement effect of the distribution information. For example, in some cases only moving images from the 10th second out of 20 seconds of moving images can be received. In particular when the receiving terminal is moving, it is difficult to remain in the narrow communication area just to receive the distribution information from the beginning, and the above mentioned problems tend to occur.